1. Field of the Invention
The invention in general relates to semiconductor device fabrication, and more particularly to a new material useful in semiconductor devices for many purposes, such as to prevent interdiffusion at silicon/metal interfaces.
2. Statement of the Problem
As is well-known, integrated circuits, often called semiconductor devices, are generally mass produced by fabricating hundreds of identical circuit patterns on a single semiconducting wafer, which wafer is subsequently sawed into hundreds of identical dies or chips. While integrated circuits are commonly referred to as "semiconductor devices" they are in fact fabricated from various materials which are either electrical conductors, such as aluminum or tungsten, electrical non-conductors, such as silicon dioxide, or electrical semiconductors, such as silicon. Silicon, the most commonly used semiconductor material, can be used in either the single crystal or polycrystalline form. In the integrated circuit fabrication art, polycrystalline silicon is usually called "polysilicon" or simply "poly". The electrical conductivity of both forms of silicon may adjusted over a wide range of conductivities by adding impurities to it, which is commonly referred to as "doping".
In the state-of-the-art semiconductor devices, it is common for the design to require interfaces of silicon and a metal such as aluminum or tungsten. For example, aluminum and tungsten are commonly used as the material of choice for electrical contacts, which contacts interface with electrically active areas made of doped silicon. It is also common in the fabrication of semiconductor devices to anneal the devices at elevated temperatures, such as 500.degree. C. At these temperatures the metal and silicon will rapidly interdiffuse into each other at the interface. Even at room temperature, the metal and silicon will interdiffuse over time. Such interdiffusion changes the semiconductive properties of the silicon and causes defective devices. Thus it is common practice to provide a diffusion barrier at silicon/metal interfaces in semiconductor devices. A thin film of titanium nitride (TiN) or titanium tungsten (TiW) are conventionally used as diffusion barriers. Such diffusion barrier films are typically of the order of 200.ANG.-1000.ANG. thick.
Conventional diffusion barriers, while generally effective at room temperature, tend to fail at more elevated temperatures. Many preferred semiconductor fabrication processes, such as deposition, reflow, and annealing, require elevated temperatures. Thus conventional diffusion barriers can create limits on the processes that can be used to fabricate a semiconductor device. There is a need for a diffusion barrier that is more effective than conventional barriers, especially at elevated temperatures.
The advantages of building integrated circuits with smaller individual circuit elements so that more and more circuitry may be packed on a single chip are well-known: electronic equipment becomes less bulky, reliability is improved by reducing the number of solder or plug connections, assembly and packaging costs are minimized, and improved circuit performance, in particular higher clock speeds. As the density of circuitry increases, the contacts used in the devices develop high aspect ratios; that is, they become deeper and narrower. Conventional deposition techniques, e.g. sputtering, have difficulty coating such deep, narrow recesses, because the atoms tend to contact one of the walls before reaching the bottom of the recess. Thus, with respect to diffusion barriers, the use of conventional production techniques, such as sputtering, leads to a decrease in the thickness of the diffusion barrier at the base of a contact as the aspect ratio increases. As the thickness of the diffusion barrier decreases, the ability of the diffusion barrier to withstand thermal energy introduced in subsequent processing decreases, and the reliability of the device degrades. Thus there has been an impetus in the industry toward new barrier technology that will deposit an adequate barrier in high aspect ratio contacts, which impetus has tended toward the development of equipment and materials not presently used in semiconductor device fabrication. Generally, a change in one phase of the fabrication process usually impacts other phases. Since semiconductor device fabrication processes are highly complex and require sophisticated equipment, developments or entirely new o processes and materials can be quite costly. Thus a diffusion barrier that is more effective and yet can be incorporated into current fabrication technology would be highly desirable because expensive modification of equipment and processes can be avoided.
3. Solution to the problem
The present invention provides a semiconductor device material comprising titanium/aluminum/ nitrogen (TiAlN) alloy. The TiAlN alloy of the invention is more effective as a diffusion barrier than the conventional TiN diffusion barriers.
The TiAlN etches readily in NH.sub.4 OH/H.sub.2 O.sub.2 similar to TiN and can be fabricated using standard sputtering equipment, therefore it can be easily incorporated into existing fabrication technologies.
The invention also provides a material that has a greater thermal budget than prior art diffusion barrier materials, thus it is more compatible with high temperature process, such as high temperature sputtering, aluminum melting/reflow using lasers or some other heating procedure, and annealing.
The TiAlN semiconductor device material according to the invention is thermally stable i.e. resistant to diffusion at high temperatures, thus preventing resistance changes, formation of undesirable precipitates which may make etching difficult, and facilitating a larger process window. Furthermore, because TiAlN is more effective as a barrier than prior art materials and has a higher thermal budget, a thinner diffusion barrier can be used. Thus the invention allows the use of conventional techniques to deposit the barrier films in high aspect ratio contacts.